(1) Field of the Invention
The present invention relates to telephone subscriber loop power supplies and more particularly to a program controlled system which supplies all of the loop circuit power requirements.
(2) Description of the Prior Art
Telephone subscriber loop circuits require a wide variety of control voltages, for such functions as talking battery, ringing, coin collect, coin return, etc. Typical voltages for these functions are -50 V, 88 V @20 Hz superimposed on 40 V, +130 V and -130 V.
In conventional analog systems these voltages are switched through the network from service circuits specially designed to provide these functions. This technique is generally not possible with a digital network because the relatively high voltages involved cannot be passed through the network. It is possible to use an analog serice network completely separate from the digital network but this approach is not economical for small remote digital offices.
Another solution has been to apply these voltages at the line card. It is not practical to employ a single line card to switch in all of the required voltages since not all lines require all voltages, the approach has been to use different line circuits for different applications. This requires a multiplicity of different line circuits which is not an economical solution in terms of both initial cost and maintenance.
The present invention solves this problem by using small low-cost digitally programmable power supplies associated with each line to supply all of the power requirements of the subscriber's loop circuit.
Accordingly, it is the object of this invention to provide an economical solution to the problem of supplying subscriber loop circuit power requirements without the need for specialized line circuits, service circuits or analog networks.